<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>元素屏幕居中</title>
<style>
	*{ margin:0; padding:0; }
	body{ height:2000px; }
	.main{ width:200px; height:100px; border:1px black solid; 
		margin:10px auto; }
</style>
</head>
<body>
<div class="main"></div>
</body>
</html>
